Terraform Module Outputs

 ✅ Importance of Terraform Module Outputs 

Terraform module outputs are a powerful mechanism to expose values from a module to its calling code. These outputs act like return values in programming, allowing higher-level modules or root configurations to reference results from reusable components. 

 

🧠 Why Outputs Are Important 

Purpose	Description
Expose values to parent modules	Share IDs, ARNs, DNS names, etc., from child modules (like VPC ID, subnet IDs)
Use output values in other resources	Chain dependencies across modules (e.g., use a VPC ID from one module in another)
Enable cross-module communication	Output of one module can become an input to another (e.g., EKS outputs feed into ALB module)
Debugging and visibility	Print values to console after terraform apply to confirm resource creation
Automation & CI/CD	Output values can be consumed in GitHub Actions, scripts, or other pipelines
Stateful resource references	Avoid hardcoding — use dynamic, dependency-aware values from the actual state

 

🧩 Example 

 

# modules/vpc/outputs.tf 
output "vpc_id" { 
 value = aws_vpc.main.id 
} 
 
output "public_subnet_ids" { 
 value = aws_subnet.public[*].id 
} 
 

 

# envs/prod/main.tf 
module "vpc" { 
 source         = "../../modules/vpc" 
 vpc_cidr       = "10.0.0.0/16" 
 public_subnets = ["10.0.1.0/24", "10.0.2.0/24"] 
 ... 
} 
 
output "vpc_id" { 
 value = module.vpc.vpc_id 
} 
 

 

📦 Example Use in Other Modules 

hcl 

CopyEdit 

module "eks" { 
 source     = "../../modules/eks" 
 vpc_id     = module.vpc.vpc_id 
 subnet_ids = module.vpc.public_subnet_ids 
 ... 
} 
 

This makes your infrastructure: 

• Composable: Each module is clean and self-contained. 

• Reusable: No need to rewrite hardcoded resource names or IDs. 

• Maintainable: Output values update automatically with the state. 

• Secure: You can choose to mark outputs as sensitive. 

 

🔐 Sensitive Output Example 

 

output "db_password" { 
 value     = random_password.db.result 
 sensitive = true 
} 
 

Terraform will hide the value in CLI output, logs, and UI. 

 

 

✅ Summary 

Benefit	Explanation
Communication between modules	Share key values like IDs, ARNs, names
Dynamic infrastructure	Avoid hardcoding and make code more portable
Easier debugging	Outputs help inspect values after apply
Better CI/CD integration	Used in scripts and pipelines
Security	sensitive = true protects secrets

 

 

📦 Full Example 

# Calling the module 
module "vpc" { 
 source = "../../modules/vpc" 
 vpc_cidr = "10.0.0.0/16" 
 ... 
} 
 
# Referencing the module output 
output "vpc_id" { 
 value = module.vpc.vpc_id 
} 
 

And in the module code itself: 

# modules/vpc/outputs.tf 
output "vpc_id" { 
 value = aws_vpc.this.id 
} 
 

 

🧠 Why This is Powerful 

Using module.vpc.vpc_id: 

• Ensures clean code without repeating resource logic. 

• Allows you to reference outputs dynamically (not hardcoded). 

• Keeps resources loosely coupled and reusable. 

 

✅ Summary 

Term	Meaning
module	Terraform's object for accessing modules
vpc	The name you gave your module instance
vpc_id	The output defined inside the VPC module